Philippine succession law, primarily governed by the Civil Code of the Philippines (Book III, Title IV) and supplemented by the Family Code of the Philippines, distinguishes between legitimate and illegitimate children in determining inheritance rights. This distinction affects both the minimum protected shares (legitime) in testate succession and the proportional division in intestate succession. The rules ensure that compulsory heirs receive their entitled portions while allowing the decedent limited freedom to dispose of part of the estate through a will.

Classification of Children

Legitimate children are those conceived or born during a valid marriage (Family Code, Art. 164), legitimated children (Family Code, Art. 177), and adopted children, who are treated as legitimate for succession purposes. Illegitimate children are those conceived and born outside a valid marriage. For an illegitimate child to inherit, filiation must be established through acknowledgment by the parent, appearance in the record of birth signed by the parent, an admission in a public document or private handwritten instrument, open and continuous possession of the status of an illegitimate child, or a final judgment in a paternity or filiation case (Family Code, Art. 172). Unacknowledged illegitimate children generally have no successional rights.

Adopted children inherit from their adoptive parents as legitimate children and may also retain certain rights from their biological parents depending on the circumstances of adoption. Posthumous children conceived before the decedent’s death but born after are considered legitimate if born of a valid marriage.

Compulsory Heirs and the Concept of Legitime

Legitimate children and their descendants, as well as illegitimate children, are compulsory heirs (Civil Code, Art. 887). They are entitled to a legitime—a portion of the estate that cannot be freely disposed of by the testator through a will, except for valid causes of disinheritance (Civil Code, Arts. 919–921). The legitime protects descendants from being unjustly deprived of inheritance.

The hereditary estate refers to the net estate after deducting funeral expenses, debts, taxes, and other administrative charges. All computations are based on this net estate.

Intestate Succession (No Valid Will or Will Does Not Dispose of Entire Estate)

In intestate succession, the entire net estate passes to the heirs according to the rules on legal succession. Legitimate and illegitimate children inherit together when both are present.

When survived only by legitimate and illegitimate children (no surviving spouse): The shares follow a 2:1 ratio. Each legitimate child receives twice the share of each illegitimate child.

Let ( L ) = number of legitimate children and ( I ) = number of illegitimate children.
Total parts = ( 2L + I ).
Share per legitimate child = ( \frac{2}{2L + I} \times ) net estate.
Share per illegitimate child = ( \frac{1}{2L + I} \times ) net estate.

If only illegitimate children survive (no legitimate descendants), they inherit the entire net estate in equal shares.

When survived by children and a surviving spouse: The surviving spouse is entitled to a share equal to that of one legitimate child. In computation, the spouse is assigned the same 2 parts as a legitimate child.
Total parts = ( 2L + I + 2 ).
Shares are allocated accordingly.

When the surviving spouse concurs only with illegitimate children (no legitimate children), the spouse is entitled to one-half of the net estate, and the illegitimate children divide the remaining one-half equally among themselves.

Testate Succession (Valid Will Exists)

The testator may dispose of the free portion of the net estate (generally one-half) subject to the rights of compulsory heirs. The will cannot impair the legitime; any disposition that reduces a compulsory heir’s legitime below the legal minimum is inofficious and may be reduced through court action (Civil Code, Arts. 906–907).

Legitime of legitimate children:
Collectively, legitimate children and descendants are entitled to one-half of the net estate, divided equally among them (Civil Code, Art. 888).
Share of each legitimate child = ( \frac{1/2 \times \text{net estate}}{L} ).

Legitime of illegitimate children:
Each illegitimate child is entitled to one-half of the legitime of each legitimate child (Civil Code, Art. 895).
Thus, the minimum share of each illegitimate child = ( \frac{1}{2} \times \left( \frac{1/2 \times \text{net estate}}{L} \right) = \frac{\text{net estate}}{4L} ).
Total minimum for all illegitimate children = ( I \times \frac{\text{net estate}}{4L} ).

This total is charged against the free portion (the other half of the net estate).

If the total claim of illegitimate children does not exceed the free portion, each receives the full computed amount, and the testator may freely dispose of any remainder.
If the total exceeds the free portion, the illegitimate children share the free portion proportionately according to their respective claims (pro-rata reduction).

The presence of illegitimate children does not reduce the collective one-half legitime reserved for legitimate children. Legitimate children always receive their full one-half first.

With a surviving spouse in testate succession:

Concurring with legitimate children: The spouse’s legitime equals the share of one legitimate child and is taken from the free portion.
Concurring only with illegitimate children: The spouse is entitled to one-half of the net estate; the illegitimate children are entitled to the other half (divided equally, subject to the pro-rata rule if numbers require reduction).

The testator may give more than the minimum legitime to any child or to third persons, provided the legitimes of all compulsory heirs are fully satisfied.

Illustrative Examples

Intestate example (no spouse):
Net estate = ₱1,200,000. Two legitimate children, three illegitimate children.
Total parts = ( 2 \times 2 + 3 = 7 ).
Each part = ₱1,200,000 ÷ 7 ≈ ₱171,428.57.
Each legitimate child receives ≈ ₱342,857.14.
Each illegitimate child receives ≈ ₱171,428.57.

Testate example (minimum shares, no spouse):
Same facts as above. Assume a will exists.
Legitime of legitimate children (collective) = ₱600,000. Each legitimate child = ₱300,000.
Each illegitimate child’s minimum = ₱150,000. Total for three illegitimate children = ₱450,000.
Free portion = ₱600,000. Since ₱450,000 < ₱600,000, each illegitimate child receives ₱150,000. The testator may dispose of the remaining ₱150,000 freely.

Testate example where reduction applies (no spouse):
Net estate = ₱1,200,000. Two legitimate children, six illegitimate children.
Each legitimate child’s legitime = ₱300,000.
Each illegitimate child’s minimum = ₱150,000. Total claim of illegitimate children = ₱900,000.
Free portion = ₱600,000. Reduction factor = 600,000 ÷ 900,000 = 2/3.
Each illegitimate child receives (2/3) × ₱150,000 = ₱100,000.

Additional Rules Affecting Computation

Right of representation: If a child predeceases the decedent leaving descendants, those descendants inherit by representation the share the predeceased child would have received (Civil Code, Art. 974). The status (legitimate or illegitimate) of the representative follows that of the person represented.
Accretion: When a co-heir repudiates or is incapacitated, the share accrues to the other co-heirs in the same class (Civil Code, Arts. 1015–1016), subject to legitime rules.
Renunciation: An heir may renounce inheritance, but advance renunciation of future legitime is generally void.
Extrajudicial settlement: When all heirs are of legal age and there is no will, or the will has been probated, the estate may be settled extrajudicially by agreement, with the same share computations applying.
Court intervention: In case of dispute over filiation, shares, or impairment of legitime, the appropriate Regional Trial Court handles the settlement of estate.

These rules apply uniformly whether the decedent is the father or the mother. The computations ensure protection of the family while respecting the decedent’s testamentary freedom within legal bounds. Proper determination of filiation and accurate valuation of the net estate are essential prerequisites to any division.